Personally, you probably have no desire to throw yourself between two buildings and into thin air, gravity, and potentially just a few seconds of regret. But you should be grateful that some people are nuts enough to do that. It leads to videos like the one above.
The whole conceit about the gang escaping from an angry security guard seems a little overdramatic (this isn't The Matrix -- some guy just doing his job isn't going to leap across rooftops to catch a couple knuckleheads), but they really are risking their lives for something to make us go whoa, so the least we could do is go whoa.
As to who those young men are and exactly what their beef with gravity is, they're part of the parkour collective Storror. It's a group of seven athletes who grew up together and have been working on this particular skill set for over a decade, according to their channel description, so probably don't try this yourself.